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p-Carborane has been vinylated on the 2-B-atom in high yields using the Heck reaction. Thus, the reaction between 2-iodo-p-carborane and various styrenes [4-H-, 4-C(6)H(4)-, 4-Cl-, 4-Br-, 4-NO(2)-, 4-CH(3)O-, and 4-CH(3)-] resulted in the production of the corresponding trans-beta-(2-B-p-carboranyl)styrene in DMF solution when reacted in the presence of silver phosphate and the palladacycle Herrmann's catalyst. 相似文献
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L. Harju Jan-Olof Lill Kjell-Erik Saarela Sven-Johan Heselius Fredrik Joachim Hernberg Alf Lindroos 《Analytical and bioanalytical chemistry》1997,358(4):523-528
Thick-target Particle Induced X-ray Emission (TTPIXE) was used for the quantitative determination of trace-element concentrations
in trunk wood. The wood samples were preconcentrated by dry ashing to improve the reliability of the sampling and the sensitivity
of the analytical method. Samples of Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) were collected from a polluted area (Harjavalta) as well as from a relatively nonpolluted area (Merimasku) in southwestern
Finland. The elements studied were P, S, K, Ca, Mn, Fe, Ni, Cu, Pb, Rb, Sr, Ba, Cd and Ag. TTPIXE combined with dry ashing
is a sensitive and reliable analytical technique for most elements studied. The method was validified by using several certified
reference materials and also by ICP-MS analysis. Due to the low ash content (0.2–0.4%) in wood a high preconcentration factor
can be obtained. Differences in trace-element uptake were observed between the two tree species studied. Trunk wood from the
polluted area contained higher concentrations of heavy metal ions.
Received: 30 August 1996 / Revised: 11 October 1996 / Accepted: 3 November 1996 相似文献
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In this study three different types of samplers for the determination of 1,6-hexamethylene diisocyanate in air were compared. The experimental set up was a simulation of real life conditions with spray painting operations performed inside a commercial, full sized, spray box. The sampling methods were 1-(2-methoxyphenyl)-piperazine impregnated on glass fibre filter, and the same reagent in impinger, and also dibutylamine in impinger. All analyses were performed by LC-MS-MS. The determined concentrations varied between 20 and 90 microg m(-3) with relative standard deviations from 7 to 17% for each method. No significant difference was found between the three methods using ANOVA with a significance level of alpha = 0.05. 相似文献
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S. Bengmark H. Thunberg T. M. Winberg 《International Journal of Mathematical Education in Science & Technology》2017,48(7):988-1001
This study examines different factors' relative importance for students' performance in the transition to university mathematics. Students' characteristics (motivation, actions and beliefs) were measured when entering the university and at the end of the first year. Principal component analysis revealed four important constructs: Self-efficacy, Motivation type, Study habits and Views of mathematics. Subsequently, orthogonal partial least squares (OPLS) analysis was used for measuring the constructs' ability to predict students' university mathematics grades. No individual constructs measured at the time of entrance predicted more than 5% of the variation. On the other hand, jointly they predicted 14%, which is almost in pair with upper secondary grades predicting 17%. Constructs measured at the end of the first year were stronger predictors, jointly predicting 37% of the variation in university grades, with Self-efficacy (21%) and Motivation (12%) being the two strongest individual predictors. In general, Study habits were not important for predicting university achievement. However, for students with low upper secondary grades, the textbook and interaction with peers, rather than internet-based resources, contributed positively to achievement. The association between Views of mathematics and performance was weak for all groups and non-existing for students with low grades. 相似文献
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The possibility of positronium induced free volume cavity expansion in some polymers above the glass transition temperature was investigated using experimental positron annihilation lifetime data from the literature for polydimethylsiloxane, polyisobutylene, and polybutadiene as function of temperature. The results suggest that free volume sites can expand towards an equilibrium size, determined as the equilibrium Ps-bubble size defined earlier for low-molecular-weight liquids. The expansion can be explained by the increase of molecular mobility and hence decrease of relaxation times, which at the higher temperatures approach the o-Ps lifetimes. Nanoscale viscosities were estimated using Navier-Stokes equation and were found to be several orders of magnitude lower than the macroscopic viscosity at the same temperature. 相似文献
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Karl Johan Winberg Gemma Barber Ludvig Eriksson Francesc Teixidor Vladimir Tolmachev Clara Vi as Stefan Sj berg 《Journal of organometallic chemistry》2003,680(1-2):188-192
We have recently shown the feasibility of palladium-catalyzed isotopic exchange between [125I]iodide and 2-iodo-para-carborane. In this work we have modified the methodology and extended its application to a wider range of iodinated carboranes. Thus, by using Herrmann's catalyst in toluene at 100 °C, 2-I-p-, 3-I-o-, 9-I-o-, 9-I-m-carborane, 1-phenyl-3-I-o-carborane and 1,2-diphenyl-3-I-o-carborane have been radiolabeled with 125iodine in high to excellent yields. 相似文献
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The direct olefination of 1,4-dien-3-ones remains a synthetic challenge. A two-step protocol, employing acetylide addition followed by catalytic Meyer-Schuster rearrangement has been developed for the olefination of 1,4-pentadien-3-ones to afford [3]dendralenes. Many of the traditional methods for the Meyer-Schuster rearrangement of alkynyl carbinols are not suitable with these highly unsaturated substrates because of their acid sensitivity. Unexpected reactivity during attempted rearrangement, including Nazarov-type electrocyclizations, is presented, along with conditions to promote the Meyer-Schuster rearrangement of ethoxyacetylene adducts using catalytic VO(acac)(2). 相似文献
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Extraction of the dried fruits from the cannon ball tree, Couroupita guianensis Aubl., yielded 6,12-dihydro-6, 12-dioxoindolo[2,1-b]quinazoline (tryptanthrin), 1a as well as indigo (7) indirubin (8a) and isatin. Compound 1a could readily be synthesized by condensation of isatin with isatoic anhydride (6) in pyridine. 相似文献